1. Field of the Invention
The present invention relates to a moveable object carrier, lithographic apparatus and a device manufacturing method, and more in particular to a system configured to carry and move an object in a plane.
2. Description of the Related Art
Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device may be used to generate a desired circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist).
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
A number of components such as the patterning device and the substrate need to be positioned at specific locations in a lithographic apparatus before processing, (e.g. a substrate on a substrate carrier to a position in an illumination path). Thereto, the lithographic apparatus comprises a number of actuators connected to carriers. In a prior art lithographic apparatus, the substrate carrier is connected to a linear actuator to move the object carrier in a first direction, which linear actuator is horizontally spaced apart from a center of gravity of the object carrier.
Since conventional linear actuators are horizontally spaced apart from the center of gravity of the object carrier, the line of action of the gravity on the object carrier lies beside the linear actuator. Thus, a moment of force is exerted on the object carrier and therefore, the linear actuator cannot fully support the object carrier such that the object carrier does not fall. Additional bearing is needed to support the object carrier. In the prior art lithographic apparatus, an air foot, i.e. an air bearing, and a stone are included to support the object carrier, requiring additional costs. Despite the additional bearing, there are high bearing loads, for example due to horizontally tilting of the object carrier, present on the linear actuator limiting the maximum acceleration of the object carrier. Further, expensive linear actuators arranged for such high bearing loads are required.